In the Province of Río Negro, Argentina, human cases of hantavirus pulmonary syndrome (HPS) have occurred in the region of the Patagonian Andean range. The Andes virus has been identified in the region, both in the rodent Oligoryzomys longicaudatus and in human beings, demonstrating mainly transmission from rodents to human and the possibility of person-to-person transmission. The goal of this paper is to present new information on hantavirus rodent carrier species in Argentina, the prevalence of antibodies to hantavirus (1999-2001 period) and the relationship of the rodent population size and seroprevalence with the occurrence of human cases (1996-2001 period). To this end, a total of 3,973 Sherman type traps for capturing live rodents were placed in six campaigns from October 1999 to May 2001. Rodent blood samples were obtained and processed by means of enzymoimmunoassay with antigens developed from the Andes virus. A summary of results indicates 397 captured rodents, with a 10% trapping success rate and a 1.0% prevalence of antibodies to hantavirus. Considerable differences were observed in species captured in each region. Seropositive O.longicaudatus and A. olivaceus specimens, as well as potential hantavirus O. flavescens and C. laucha carriers, were captured. Six human cases were recorded during the 1993-1995 period (corresponding to retrospective studies), while 21 cases were reported in 1996-1998 and 6 in 1999-2001. The correlation between occurrence of human cases, seroprevalence in rodents and trapping success is analyzed.